At the non-phosphoric ends of two matches cut a small notch so that they fit into each other. Stretch the matches apart so as to form an angle, and place them vertically upon the table. Then lean a third match against them so as to form a tripod, standing by itself.
The question now is to take up this trivet with a fourth match and carry it to another place without disturbing the harmony of the little construction.
At first sight this seems impossible; it is, however, easily done. You have only to slide the fourth match between the two stuck together, and the one serving as support.
By lightly pressing against the two first ones the third one will slide, and its upper extremity will come between the angle formed by the two others. By taking it up briskly, this extremity will be maintained, and you are then enabled to carry the little tripod to another place.
The Distance of an Inaccessible Point.
Everyone knows what an angle is, and you say at once it is the inclination of two lines that meet each other. These lines by their branching off form an opening more or less wide. This opening is measured by the aid of an instrument called a protractor made of brass or horn, which finds its place in nearly every box of mathematical instruments.
It represents a semi-circumference, divided into 180 equal parts, called degrees, written thus: 180°. Each degree is divided into 60 minutes, expressed thus: 60 min.; and finally the minutes are divided again in 60 parts, called seconds, indicated thus: 60 sec. There are therefore in a whole circumference, 360 deg., 2,160 min., and 12,960 sec.
One degree, therefore, is the 360th part of a circumference, and thus we have a measure independent of all dimensions. For example, on a round table of 36 yards in circumference, one degree will be marked by one tenth of a yard; on a pond of 360 yards in circumference, one degree will be equal to one yard.